It has previously been recognized that boats and other watercraft operate better with adjustable trim tabs. Trim tabs are typically mounted at the stern of the vessel and are controllably extended to affect the flow of water passing about the vessel. The attitude or orientation of the watercraft is thereby affected.
Most prior trim tab systems employ hydraulic rams which extend port and starboard trim flaps. The trim flaps are extended downwardly to lower the bow of the boat. An example of such a system is shown in U.S. Pat. No. 3,695,204.
Hydraulic trim tab systems have suffered from certain limitations. Foremost is the relatively abrupt action of hydraulic trim tabs which oftentimes result in an uncomfortably abrupt change in boat attitude. Hydraulic systems also employ oil which can be messy and polluting.
Prior art boat trim systems also used a singular pump or other source of pressurized fluid. This source is then valved to the respective port and starboard trim tabs. Such an arrangement allows pressure communication between the port and starboard actuating rams even though they are intended to be of independent operation.
Thus there remains a need for an improved watercraft trim system which provides improved performance, clean operation, enhanced boat stability and smooth operation.